I was reading a thread a while back when you were all talking about concrete flooring in your basements. I read with interest because I have been exercising for 15 years on carpet and pad over concrete. I usually get along fine, but occasionally my knees and sometimes my shins bother me a little. I went to my local IFA and purchased 2 4x6 stall mats. I exercised on them yesterday and my question is, do your stall mats move when you are exercising? Mine are sitting on top of my carpet and even though I put weight plates on each corner they still move. Any suggestions? I do like them and I feel like they lessen the impact on my knees. Good thing since my current rotation is CTX. (This is my first time posting, I have been lurking for months and learned so much from this "educated crowd"!!)